Standardize headers and docstrings (#4417)

* Implement new headers

* Reformat 1

* Reformat 2

* Reformat 3 - math

* Reformat 4 - yaml

export.py

@@ -1,4 +1,6 @@
-"""Export a YOLOv5 *.pt model to TorchScript, ONNX, CoreML formats
+# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
+"""
+Export a PyTorch model to TorchScript, ONNX, CoreML formats
 
 Usage:
     $ python path/to/export.py --weights yolov5s.pt --img 640 --batch 1